The circuit shown provides an input to a transistor: A transistor is a type of electronic switch and in this circuit it can be assumed to have infinite resistance; 7.0 V The resistance of the LDR varies with light level as shown below - Edexcel - A-Level Physics - Question 13 - 2023 - Paper 1

To determine the resistance of the Light Dependent Resistor (LDR) at 30 lux, we can refer to the graph provided. The graph indicates that when the light level is at 30 lux, the corresponding resistance is approximately 3000 Ω.

Next, we will calculate the potential difference across the LDR.

Using the voltage divider rule, we have:

$V = 7.0 \times \frac{R_{LDR}}{R_{LDR} + 333}$

Substituting the values:

$V = 7.0 \times \frac{3000}{3000 + 333} = 7.0 \times \frac{3000}{3333} \approx 6.3 V$

The potential difference across the LDR is approximately 6.3 V, which is above the 0.7 V threshold necessary for the transistor to turn on.